J. Kerry Thomas

Encapsulation of TiO2 in zeolite Y

Abstract A new method of incorporating TiO2 into zeolite cavities through ion exchange of zeolites Y with an aqueous solution of ammonium titanyl oxalate oxalate monohydrate, (NH4)2TiO(C2O4)2H2O, has been developed. Characterization of the products clearly demonstrates that (1) ion exchange between the Ti species present in the solution and the cations in the zeolites takes place; (2) the Ti species are located inside the zeolite cavities, but not on the external surface of the zeolite; and (3) the Ti-species encapsulated are TiO2 clusters of various small particles sizes and have characteristics of the TiO2 semiconductor.

Preparation, characterization and photoreactivity of titanium(IV) oxide encapsulated in zeolites

The preparation, characterization and photoreactivity of titanium(IV) oxide encapsulated inside either sodium- or ammonium-exchanged zeolite Y (NaY and NH4Y), mordenite (NaM and NH4M) or potassium zeolite L (KL) are presented. The material was prepared by an ion-exchange method with ammonium titanyl oxalate monohydrate aqueous solution, (NH4)2TiO(C2O4)2·H2O. The results of X-ray photoelectron spectroscopy, chemical analysis and photolysis studies support the contention that the exchanged titanium species locate dominantly inside the zeolite cavities, and not on the external surfaces. The TiO2+-exchanged zeolite exhibits characteristics of TiO2, such as photoreduction of methyl viologen to methyl viologen radical cation. A significant blue shift of the UV–VIS reflectance spectrum (onset ca. 330 nm), compared with those of bulk anatase and rutile TiO2, and a lack of an X-ray diffraction pattern of TiO2 in the TiO2–zeolite samples indicate that the particle size of the TiO2 encapsulated inside the zeolite is on the nanometre scale.

Photophysical and photochemical properties of CdS with limited dimensions

Laponite, porous Vycor glass and molecular sieves, faujasite X and sodalite, have been used to prepare small particles of CdS with limited dimensions. Laponite limits one dimension of the CdS particles by the interplaner spacing of 11.5 A. Porous Vycor glass limits two dimensions of the CdS particles to < 40 A. Molecular sieves were used to limit the particle size to the size of the cavity; however, the particles constructed were larger than the cavity dimensions. The absorption onset and main emission wavelength increase with increasing Cd2+ concentration. The spectral properties of PbS are also reported. Methyl viologen and Cu2+ quench two different emission bands arising from CdS on laponite in solution. Methyl viologen quenches the high-energy emission, thought to arise from exciton recombination, while Cu2+ efficiently quenches a low-energy emission thought to arise from S2– deficiencies. Methyl viologen shows dynamic-type kinetics, while the static-type kinetics observed from Cu2+ gives an estimate of the particle size. The spectroscopic properties of the particles are studied as a function of cadmium concentration and discussed in terms of particle size.

Interaction of lysophosphatidylcholine with phosphatidylcholine bilayers. A photo-physical and NMR study.

Several photo-physical methods together with 31P-NMR have been used to investigate the effect of lysophosphatidylcholine on phosphatidylcholine bilayers. 31P-NMR shows that the permeability of the vesicle to Eu3+ increases sharply above approx. 40% lysophosphatidylcholine: fluorescence-quenching studies also show this type of behavior. Similar sharp changes in vesicle properties are observed via the photo-physical technique at this lysophosphatidylcholine/phosphatidylcholine composition. Fluorescence spectra of pyrene and pyrene carboxaldehyde show that increasing lysophosphatidylcholine composition increases the polarity of the environments of these probes up to 40% lysocompound. Above this composition the photo-physical properties of the probes slowly revert to those characteristic of the micellar lyso-compound. The pyrene fluorescence lifetime, the fine structure of the fluorescence, and the case of formation of pyrene excimer in these bilayer mixtures suggest that pyrene complexes weakly with the charged nitrogen of the choline group of the phosphatidylcholine and that the physical state of the system has a striking effect on this complexation process. Similar experiments with simple quaternary compounds lend strong support to this suggestion. The studies monitor in several ways the effect of bilayer composition on movement of molecules in these systems. The degree or site of solubilization of carcinogens is also uniquely affected by composition.

Photophysical studies of pyrene in micellar sodium taurocholate at high salt concentrations

Abstract The photophysics of excited pyrene solubilized in micellar sodium taurocholate (NaTC) has been studied by transient emission and absorption techniques. The fine structure of the fluorescence spectrum indicates complicated behavior of the surfactant in the absence of high salt concentrations. Conventional micellar behavior was observed in NaCl concentration of 1 M , and here excited pyrene is efficiently quenched by cetylpyridinium chloride (CPC1) and N,N -dimethylaniline (DMA) via an intramicellar mechanism. Similar behavior has been observed previously for sodium lauryl sulfate (NaLS), and analysis of the data produced an aggregation number of 18 ± 3 for sodium taurocholate in 1 M NaCl. Excited pyrene in NaTC in 1 M NaCl is also quenched by several inorganic cations, and the kinetics follow a Stern-Volmer relationship. The derived quenching rate constants were independent of the micellar concentrations. These data suggest that the quenching occurs via simple collisional dynamics, and is quite unlike the behavior observed for these photosystems in micellar NaLS, where the reactions are still intramicellar. Quenching of excited pyrene by Cu 2+ leads to the pyrene cation and Cu + , while quenching by DMA leads to the pyrene anion and DMA cation. The yields of photo-produced ions are higher in micellar NaTC than in micellar NaLS, and compare favorably with the yields in methanol-water mixtures or in aqueous caffeine solutions. The mechanism leading to photo-induced electron transfer and subsequent escape of ions is discussed, and emphasis is placed on a comparison of micellar NaTC and NaLS.

PHOTOIONIZATION OF NAPHTHALENE, TRANS-STILBENE AND ANTHRACENE ADSORBED ON THE EXTERNAL AND INTERNAL SURFACES OF ZEOLITES

Abstract Laser photolysis of anthracene, naphthalene and trans -stilbene on zeolite NaA and in zeolite NaX produces electrons trapped in Na n n + clusters, singlet and triplet excited states and radical cations of the arenes. Only Na 4 3+ is observed in NaX where the arene is located inside the supercage; however, other trapped species, such as Na 3 2+ , are also observed in NaA where the arene is located solely on the external surface. Thermal decomposition of trans -stilbene in NaX produces an unknown brown product, which shortens the lifetime of the electrons trapped in the sodium ionic clusters. The photoionized electrons from arenes on NaA are trapped by sodium cation clusters inside the sodalite cage next to the surface and close to the arene radical cation. No oxygen quenching of the trapped species, Na 3 2+ and Na 4 3+ , in the arene—NaA system is observed due to the exclusion of O 2 by the small entry pore of the sodalite cage (approximately 2.6 A).

Mobility and reactivity in colloidal aggregates with motion restricted by polymerization

Vesicle systems containing polystyrene or cross-linked polystyrene have been examined for the effect the presence of the polymer has on the physical properties of the vesicles, the lateral mobility of probe molecules in the plane of the bilayer and the diffusion of molecules across the bilayer. Differential scanning calorimetry of these vesicles, as well as vesicles containing monomer, and vesicles containing the polymer show the phase transition of hydrocarbon chains characteristic of a bilayer, to be present in all cases. Fluorescent probes show an increased lateral mobility when the monomer is introduced into the vesicle and a decreased lateral mobility when the vesicle contains the cross-linked polymer. Transbilayer movement of n.m.r. shift reagents is not markedly affected by the presence of polymer.

Radiation induced physical and chemical processes in zeolite materials

Abstract Ionic processes induced by high energy radiation in zeolites, including electron and hole trapping and related chemical reactions, are reviewed in this paper. Electronic structures of electrons localized in clusters of charge balancing cations and those solvated in zeolite confined water clusters are characterized by a combination of spectroscopic techniques such as ESR and transient UV–visible absorption. Reactivities of these trapped electron species confined in a nanometer dimension are understood in correlation with their structural characteristics. Positive charge transfer from the zeolite framework to molecular adsorbates and subsequent oxidation reactions are also examined.

Photophysical properties of pyrene in zeolites. Observation of pyrene anion radicals in zeolites X and Y

Abstract Formation of pyrene anion radicals in the supercages of zeolites X and Y on photoexcitation is observed by using direct time-resolved diffuse reflectance spectroscopy, and the pyrene anion radical is found to co-exist with the pyrene cation radical.

The temperature dependence of the triplet lifetimes of some aryl iodides and bromides

A variable temperature pulse radiolysis study of the triplet state of iodonaphthalene and iodobiphenyl indicates that an intramolecular energy relocation process is inhibited as the temperature is lowered from 20 °C, resulting in a lengthening of the lifetime of the triplet state. It is postulated that the triplet state energy of these aryl iodides is channeled into the C–I bond, causing bond dissociation. The activation energies for this process, in toluene, have been measured to be 5.9, 4.8, and 3.4 kcal/mole for 1‐iodonaphthalene, 2‐iodonaphthalene and 4‐iodobiphenyl, respectively. Similar experiments with aryl bromides in toluene, at temperatures greater than 20 °C, are also interpreted as indicating the dissociation of the C–Br bond from the triplet state. For 4‐bromobiphenyl and 4,4′‐dibromobiphenyl the activation energy is in the range of 10–13 kcal/mole. The results are discussed in relation to the work of Bersohn and co‐workers.